Method of producing aromatic hydrocarbons



Patented Apr. 20,

METHOD OF PRODUCING AROMATIC HYDROCARBON Paul H. Johnson, Bartlesville,kla., and Robert R. Parker, Berger, Tex., assignors to PhillipsPetroleum Company, a corporation of Delaware Application October 30,1944, Serial No. 561,118

3 Claims. (01. 260-6735) matic materials boiling in the motor fuel rangeor by converting a portion of the parafflnic material in the motor fuelor material from which it is derived, to aromatics boiling in the motorfuel range. In order to convert paramnic materials to suitable aromaticcompounds it is usually necessary to carry out a series of complexthermal and/or catalytic reactions and as a necessary consequencethereof certain losses occur dueto carbonization and conversion intoproducts which are outside of the desired boiling range. Certain otherdisadvantages result from the necessity for carrying out these reactionsat elevated temperatures and the necessity for supplying or abstractingheat in these reactions. Applicants have now discovered a method forincreasing the aromaticity of parafllnic materials in a simple andeconomic manner.

It is an object of this invention to pass a preheated hvdrocarbon chargethrough a catalyst chamber having a plurality of appropriate catalystbeds separated by thermal cracking zones to cause successive thermal andcatalytic reactions in the charge to increase the aromatic hydrocarboncontent thereof.

A more specific object of this invention is to subject heatedhydrocarbon oils to alternate thermal and catalytic reactions underconditions where the paraffin content of the charge is converted tooleflns, the olefins reacted to form aromatics, the mixture againtreated to form additional olefins which again are reacted to formaromatic hydrocarbons, and these reactions alternately caused to takeplace in a continuous flow of hydrocarbons to substantially increase thearomatic content of the original charge.

Another object of this invention is to provide a method which takesadvantage of the fact that the reaction of the oleflns to form aromaticsis an exothermic reaction and the formation of olefins from paraflins isan endothermic reaction and thus each reaction may be carried out in amanner which will wholly or partially compensate for the temperaturechange occurring in the other. Further advantage is taken of the factthat the aromatics which are formed are relatively stable undertheconditions where the oleflns are formed from unreacted paraiiins so thatthe addition of successive increments of aromatics is eflected withoutdestruction of the aromatic compounds formed during previous reactions;

Other and more detailed objects of this invention will be apparent fromthe following disclosure of one method of practicing it.

This invention resides in the steps and series of steps of the methodherein disclosed.

In general the charge stocks converted in the present process are highlyparaflinic materials, the aromaticity of which it is desired toincrease. Such-materials include light naphthas boiling in the range of,say, 200 to 400 F., straight run gasolines, and highly paraflinicfractions from various sources such as the C1 and higher materialsfractionated from natural gasoline. In accordance with applicantsinvention these materials are subjected to alternate thermal andcatalytic reactions in a series of zones located within the samereaction chamber or in contiguous or heat exchange relationship. In thethermal zones dehydrogenation of parafllnic materials to olefins occursas a primary reaction and these olefini-c materials are successivelyaromatized by cata- -lytic reaction to form aromatics. At the same timesome cracking, particularly of heavier paramns, also occurs. Thedehydrogenation-cracking reaction to form olefins is endothermic whilethat for the conversion of olefins to aromatias has been found to beexothermic.

The invention may be carried out by arranging in areaction chamber aseries of alternate thermal and catalytic zones. The thermal zones maybeopen spaces or may contain relatively inert contact material of thenature of firebrick, Alundum, or silicon carbide. These zones should beof sufiicient dimension to provide the desired contact time necessary toeffect thermal dehydrogenation and cracking at the flow rate of chargewhich is used. The catalyst zones contain a desired catalyst foreffecting aromatization and this catalyst should be one which would bespecific enough for aromatization and polymerization reactions to resultin a net exothermic effect. Such catalysts include bauxite.silica-alumina, and chromium oxide alone or preferably activated byadmixture with oxides of aluminum, iron, molybdenum. thorium and thelike; Heavy metal salts may also be used. Among these may be mentionedthe molybdates and tungstates of nickel, vanadium, chromium and iron. Inparticular it has been found that the use of bauxite will result in asubstantial exothermic reaction at the temneratures'and under theconditions described herein and that this exothermiclty may under Iversion zone is oi. such dimensions as to permit a temperature drop of50 F. to take place, the catalyst and dimensions of the catalytic zoneare so selected as to permit a temperature rise in that zone orapproximately 50 F. so that when the eifluent from that zone enters thenext thermal conversion zone it will have been elevated to the desiredinitial conversion temperature. The temperature drop in this nextthermal conversion zone may be compensated for by the temperature risewhich occurs in the succeeding catalytic zone. Thus the two reactionsmay be carried out without the necessity for supplying additional heatto the endothermic zones or removing heat from the exothermic zones.

Further control of temperature or reaction time in the respective zonesmay be obtained by the use of an inert diluent such as steam which may,if desired, be heated to an extent sufllcient to provide for removing orsupplying the desired amount of heat to or from the respective zones.Thus in case the temperature drop or temperature rise,as the case maybe, in any zone is insufflcient to compensate for the change intemperature of the preceding or succeeding zone, the deficiency may becompensated for by the use of heated diluent. Inasmuch as the use ofdiluent will decrease contact time it may be desirable to compensate forthis decrease by increasing the depth of the successive zones inproportion to the concentration' or diluent. It is also frequentlydesirable to add diluent to the feed entering the thermal conversionzones in order to maintain the contact time therein sufiiciently low topromote olefin formation. This will of course necessitate an increase inthe depth or the catalyst zones in order to provide a suihcient contacttime to permit substantial aromatizing to take place.

Ordinarily, the dehydrogenation reaction is conducted at a slightlyhigher temperature than the aromatizing reaction, for example, with atemperature in the range of about 1000 to 1200 F. for the thermaldehydrogenation reaction is purely thermal, so that the aromatizationreaction will be conducted at a slightly lower initial temperature dueto the temperature drop in the preceding zone. Because of practicalconsiderations the extent of this temperature drop should preferably notbe greater than about 100 F. In order to obtain substantial olefinformation in the dehydrogenation zone a contact time of 0.05 to 1 secondmay be used, while in the aromatization zone a contact time of 0.5 to 2seconds may be provided. 1

In the accompanying drawings the single figure is a diagrammaticillustration of an apparatus suitable for illustrating the proceduralsteps of the method herein claimed.

In accordance with this invention a catalyst chamber or case i isemployed of any suitable and well known construction in which aplurality of catalyst beds C of suitable catalyst are supported onperforated or permeable supports S in spaced relation, as shown in thedrawing, to

, 4 form spaces or voids Vbetween the catalyst beds. Thus it is clearfrom the, drawing. in relation to the flow path of the charging stock,that it passes alternately through the voids or spaces and the catalystbedsas it progresses fromthe inlet of the catalyst case to the outlet.

The charging stock is preheated before delivery to the catalyst casein apreheater ll of any suitable construction. The charging stock issupplied ftom the source through the line l2 to the heating coils I! ofthe preheater and from there through the line It into one end of thecatalyst case l0. As will be described later, 'a suitable diluent may beadded to the charging stock through the line I5 for admixture therewithbefore preheating and/or the same or a different diluent may beintroduced into the charging stock at one or more reaction zones in thecatalyst case through the line l8 and its branches. The reacted fluid iswithdrawn from the catalyst case l0 and delivered to any suitableseparating or fractionating equipment, not shown, by the line H. Thecontemplated reactions are carried out in the catalyst case underpressures from 0 to 200 pounds per square inch, and therefore, thevarious lines are suitably valved and controlled in an obvious manner tomaintain the selected operating Pressure.

In one actual demonstration of this process, the hydrocarbon oilcharging stock, which was a light naphtha containing mainly paraflins,some oleflns, some aromatic hydrocarbons and other cyclic compounds suchas cycloparaifins, was supplied to the preheater H where its temperaturewas raised to approximately 1140 F. The charge stock had a boiling rangeof about 200-400 F. In this operation the charging stock was dilutedwith steam in the weight ratio of oil to steam or about 6 to 1, and themixture was fed at the rate of 8 to 10 barrels of oil per hour.

The catalyst employed was 10-20 mesh granular bauxite although othercatalysts as described may be used in this process. In the particularoperation described the catalyst beds were about 3 feet in diameter andprogressively increased in depth 1mm 2 feet at the top to 4 feet at thebottom. The thermal spaces varied in depth from 2 feet at the top to 3feet at the bottom.

Oleiins are formed in the mixture while in the first space V and underthe temperature and pressure conditions and flow rate noted. Someolefins, of course, may be formed in the reheater and in the line H onthe way to the catalyst case. The mixture then proceeds through thefirst catalyst bed C where a portion of the olefins present in themixture is converted into aromatic hydrocarbons. tion in the firstspace, which is a thermal reaction, heat is absorbed since this is anendothermic reaction. However, during the reaction in the catalyst bed,which is of course a catalytic reaction, heat is given oiI since this isan exothermic reaction. Therefore the temperature or the mixture in thecatalyst bed rises. When the mixture proceeds to the next space Vfurther oleflns are formed and the temperature falls to be followed byan increase in temperature of the mixture during the formation ofadditional aromatic hydrocarbons from the olefins just formed. Thesealternate reactions continue as the mixture moves through the catalystcase and the percentage of aromatic hydrocarbons present graduallyincreases in view of the fact that under the conditions noted previouslyformed aromatic hydrocarbons are stable during During the reaczone andin the absence of any catalyst for a time of 0.05 to 1 second, passingthe resulting material production of 11.15% of aromatic hydrocarbons.

The resulting mixture was through the line H, first, to suitableseparating equipment to remove the diluent steam therefrom, and then tosuitable fractionating equipment of conventional form to fractionate theproduct in accordance with the uses to which it was to be put. Theresultant product in this case is very valuable as an ingredient ofhighoctane high-rich rating aviation gasoline.

As noted in the example above, no additional heated diluent was added tothe spaces through the line l0 and its branches but where it is desiredto vary the reaction time this can be controlled by the volume of theheated diluent introduced directly into the spaces through the line IEor its branches, either as an addition to that added to the mixturethrough the line 15 or as an alternative thereto. Thus reaction time aswell as temperature may be controlled in whole or in part by the use ofdiluent at a predetermined volume or temperature. It is to be noted thatin addition to steam other inert gases such as nitrogen or methane canbe used for the same purpose. It is also within the purview of thisinvention to employ heating coils in the spaces V for supplying heat tothe thermal reaction an thereby controlling the reaction time.

To be more specific with regard to the example described above, thefollowingobservation tem-- peratures are noted remembering. that thecharge stock was delivered into the reaction chamber at a temperature of1140 F. The temperature in the first catalyst bed averaged about 1100 F.and in the first space below it about 1075 The temperature of themixture in the upper part of the second catalyst bed was 1090 F. and inthe lower part 1100 F. The temperature in the next space V was 1080 F.and in the upper part of the next catalyst bed 1077 F. At about thecenter of this bed it was 1076? F. In the next, that is the last spaceV, the temperature was 1087 F. In the upper part of the last catalystbed it was 1095" F., at the center 1097 F. and near the bottom 1093 F.Thus it will be seen that by alternate thermal and catalytic reactionsthere was very little total then passed loss of heat in the charge asbetween the top of the first catalyst bed and the bottom of the lastone.

From the above description it will be apparent to those skilled in theart that the method herein disclosed is capable 01' some variationwithin the novel scope thereof without departure from the true subjectmatter of the invention. We do not, therefore, desire to be strictlylimited to the illustrative example herein given but rather by thelimitation of the appended claims.

What is claimed is:

1. A process for converting a paraflin hydrocarbon material boiling inthe gasoline range to aromatic hydrocarbons, which comprises heatingsuch a material to. a temperature in the range of 1000 to 1200 F. andmaintaining same within this temperature range in an endothermicconversion containing olefins so produced into contact with a mass ofsolid granular catalyst which promotes exothermic aromatizationandpolymerization reactions for a reaction time of 0.5 to 2 seconds toeffect an exothermic hydrocarbon reaction, passing hydrocarbon-seffluent from said catalyst mass through a second endothermic conversionzone in the absence of a catalyst for a reaction time of 0.05 to 1second, passing the resulting material containing olefins so producedinto contact with a second mass of solid granular catalyst whichpromotes exothermic aromatization and polymerization reactions for areaction time of 0.5 to 2 seconds to effect an exothermic hydrocarbonreaction, each of said endothermic reactions being carried out withoutaddition of heat from an outside source, and recovering from eflluentsof the last said zone an aromatic hydrocarbon material boiling in thegasoline range so produced.

2. A process for converting a parafiin hydrocarbon material boiling inthe range of 200 to 400 F. to aromatic hydrocarbons, which comprisesheating such a material to a temperature in the range of 1000 to 1200 F.under a pressure not greater than 200 lbs. sq. in. and maintaining samewithin this temperature and pressure range in a subsequent endothermicconversion zone and in the absence of any catalyst and added heat for atime of 0.05 to 1 second and such that a tem perature fall of not morethan 50 F. takes place, passing the resulting material containingolefins so produced into contact with a mass of solid granular catalystwhich promotes exothermic aromatization and polymerization reactions fora reaction time of 0.5 to 2 seconds and such that a temperature rise ofnot more than 50 F. takes place in the absence of added heat to effectan exothermic hydrocarbon reaction, passing hydrocarbons efliuent fromsaid catalyst mass through at least one additional series of endothermicand subsequent exothermic conversion zones operated under the sameconditions as those just recited, and recovering from eiffiuents of thelast exothermic conversion zone an aromatic hydrocarbon material boilingin the gasoline range so produced.

3. A process according to claim 2 wherein the aromatization catalyst isbauxite.

. PAUL H. JOHNSON.-

ROBERT R. PARKER. I

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